Reaction Steps
To a stirred solution of nucleoside 4 (2.26 g, 4.68 mmol) in THF (12 cm3) and water (12 cm3) was added sodium periodate (3.04 g, 14.2 mmol) and a 2.5% solution of osmium tetraoxide in tert-butanol (w/w, 0.603 cm3, 40 μmol). The solution was stirred at room temperature for 45 min. Water (25 cm3) was added and the solution was extracted with dichloromethane (2×50 cm3). The organic phase was washed with a saturated aqueous solution of sodium hydrogencarbonate (3×30 cm3) and dried (Na2SO4). The solvent was removed under reduced pressure and the residue was redissolved in THF (12 cm3) and water (12 cm3). The mixture was stirred at room temperature and sodium boronhydride (182 mg, 4.71 mmol) was added. After stirring for 1.5 h, water (25 cm3) was added and the solution was extracted with dichloromethane (2×50 cm3). The organic phase was washed with a saturated aqueous solution of sodium hydrogencarbonate (3×30 cm3) and dried (Na2SO4). The solvent was removed under reduced pressure and the residue was purified by silica gel column chromatography using dichloromethane/methanol (98:2, v/v) as eluent to give 5 as a white solid material (1.13 g, 49%). δH (CDCl3) 9.29 (1 H, br s, NH), 7.47 (1 H, d, J 1.1, 6-H), 7.38-7.25 (10 H, m, Bn), 6.22 (1 H, d, J 3.4, 1′-H), 4.62 (2 H, s, Bn), 4.60 (1 H, m, 4′-H), 4.46 (2 H, s, Bn), 4.35 (1H, dd, J 3.4, 7.5, 2′-H), 3.83-3.73 (4 H, m, 2×5′-H, 2×2″-H), 2.67 (1 H, br s, OH), 2.07-2.01 (2 H, m, 2×1″-H), 1.77 (3 H, d, J 0.5, CH3). δC (CDCl3) 164.3 (C-4), 150.3 (C-2), 137.6, 137.4 (Bn, C-6), 136.7 (Bn), 128.6, 128.4, 128.2, 127.8, 127.6, 127.3, 127.1 (Bn), 108.4 (C-5), 88.0, 87.7, 81.6, 74.7 (C-1′, C-2′, C-3′, C-4′), 73.7, 69.6 (Bn), 64.6 (C-5′), 57.7 (C-2″), 28.6 (C-1″), 12.4 (CH3). FAB-MS m/z 483 [M+H]+, 505 [M+Na]+ (Found: C, 63.6; H, 6.2; N, 5.4. C26H30N2O7,0.5H2O requires C, 63.5; H, 6.4; N, 5.7%).
